QUASI-REVERSIBLE TRANSFORMATIONS IN THE ((BI,PB)O)(2)SR2-XCAXBIN-1FENO3N-PROPERTIES OF THE ARISING PHASES(1+Z (X=0 AND X=1) SYSTEM AND THEIR INFLUENCE ON THE IRON DISTRIBUTION AND MAGNETIC)

A phase analysis of the components resulting from a complex program of reactions for the preparation of ((Bi, Pb)O)(2)-Sr2-xCaxBin-1 FenO3n1+z with x = 0, x = 0 and n = 1, n = 2, using Fe-57 Mossbauer spectros copy, was performed. Whereas for the phases with n=1 only relatively s light differences in the values of the Neel temperature between 207 an d 250 K were found, the phases with n = 2 presented stronger differenc es, the magnetic ordering temperatures ranging for different condition s of reactions between 205 and 512 K. The two-phase sample with n=2 or dered magnetically below 60 K. An increase in the duration and/or temp erature of reaction resulted in compounds with a high degree of inhomo geneity in the vicinity of the Fe sites leading to a distribution of F e spin freezing temperatures. All the phases studied with n=1 exhibite d a Morin spin reorientation transition, with the spins parallel to th e c-axis at low temperatures and perpendicular to it above 100-150 K. In all the samples studied about 4%-11% Fe in the form of high spin Fe 4+ was present, the corresponding Mossbauer sextet vanishing at higher temperatures because of faster electron hopping.